OPERATING SEGMENT INFORMATION Major Products (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Revenue by major product
Net premiums earned	$ 176,918	$ 169,003
Casualty segment
Revenue by major product
Net premiums earned	108,593	98,768
Casualty segment | Commercial and personal umbrella
Revenue by major product
Net premiums earned	27,130	25,297
Casualty segment | General liability
Revenue by major product
Net premiums earned	20,013	19,972
Casualty segment | Professional services
Revenue by major product
Net premiums earned	18,538	17,080
Casualty segment | Commercial transportation
Revenue by major product
Net premiums earned	18,274	14,681
Casualty segment | P&C package business
Revenue by major product
Net premiums earned	10,900	9,649
Casualty segment | Executive products
Revenue by major product
Net premiums earned	4,835	4,685
Casualty segment | Medical professional liability
Revenue by major product
Net premiums earned	3,815	3,104
Casualty segment | Other casualty
Revenue by major product
Net premiums earned	5,088	4,300
Property segment
Revenue by major product
Net premiums earned	38,685	42,118
Property segment | Commercial property
Revenue by major product
Net premiums earned	17,596	19,903
Property segment | Marine
Revenue by major product
Net premiums earned	12,300	11,917
Property segment | Specialty Personal
Revenue by major product
Net premiums earned	6,308	6,790
Property segment | Property reinsurance
Revenue by major product
Net premiums earned	2,762	3,017
Property segment | Crop reinsurance
Revenue by major product
Net premiums earned		465
Net premiums earned	(281)
Property segment | Other property
Revenue by major product
Net premiums earned		26
Surety segment
Revenue by major product
Net premiums earned	29,640	28,117
Surety segment | Miscellaneous
Revenue by major product
Net premiums earned	11,097	10,168
Surety segment | Commercial surety product
Revenue by major product
Net premiums earned	7,354	6,901
Surety segment | Contract
Revenue by major product
Net premiums earned	6,743	6,830
Surety segment | Energy Surety
Revenue by major product
Net premiums earned	$ 4,446	$ 4,218